Caffeine and Cognitive Performance - Caffeine: Chemistry, Analysis, Function and Effects - page 273

Higher-order processes are those considered to be involved in the active
monitoring, guidance, and coordination of behavior (Bruny´ et al 2010a). An
important component of these is the ability to inhibit inappropriate actions,
and reduce the influence of interfering information. The Stroop color-word
tasks and the Wisconsin card sorting test are two neuropsychological tasks
which assess inhibitory control (executive function). In executive control or
higher-order processes tasks, the administration of low doses of caffeine does
not show significant effects independently of the profile of caffeine
consumption of the participants (Adan and Serra-Grabulosa 2010; Bruny´ et
al 2010a; Hogervorst et al 2008; Sun et al 2007; Tieges et al 2009). Some
benefits are found only with the administration of doses from 200 mg in non-
habitual consumers (Bruny´ et al 2010a) and of 400 mg in habitual consumers
of caffeine (Bruny´ et al 2010b).

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15.5 Effects of Caffeine in Subjective Activation and
Affect
The measurement of the subjective state of the individuals may be carried out
using several different self-assessment questionnaires. Among the instruments
most widely used to study the effects of caffeine there are the Stanford
Sleepiness Scale (SSS), the Profile of Mood States (POMS) and the Visual
Analogue Scales (VAS). All of them have been shown to be sensitive to the
effects of caffeine intake.
The VAS are faster to answer and facilitate the collection of information in
cases of repeated measures. Using a set of eight VAS (see Figure 15.1) designed
by our team, four scales refer to the dimension of subjective activation
(alertness, vigor, weariness and sleepiness) and four refer to affect (happiness,
calmness, sadness and tension). These scales allow us to measure adequately
and completely the participants' subjective state (Adan et al 2008b). Each scale
is 100 mm long and asks the subject to put a cross at points between "very
little" (left) and "very much" (right) based on perception at the moment of
response (scores range from 0 to 100). Each group of four scales can then be
added algebraically to give a simple global value of activation [(alert) +
(vigorous) + 200 2 (weariness) 2 (sleepiness) / 4] for activation, and
[(happiness) + (calm) + 200 2 (sadness) 2 (tense) / 4] for affect. Each scale
can

also be analyzed independently to determine whether they differ in

sensitivity to the variable studied.
The effects of caffeine on subjective state have been widely studied in human
subjects. Research has shown that caffeine consumption is reliably associated
with positive subjective effects even in the absence of acute withdrawal effects.
The subjects report that they feel more alert, efficient, jittery, vigorous, able to
concentrate and motivated to work. In contrast, the subjective perception of
sleepiness, fatigue, drowsiness, tiredness, and negative affect decreases. This
has been observed independently of the instrument used to assess the subjective
state, and has also been observed with a wide variety of doses (Adan et al